Add custom fields to Lists (Views) block

I usually do this by adding a class in the View, or in the block with https://www.drupal.org/project/block_class.

What about to use a content block and render a view in it with the module like Viewfield?

I just ran into this exact issue today, and I was not able to find a way to add/extend configuration to a views block. In the end, I went an alternate route - I created a block plugin, that has custom configuration, and renders the view.

Use case:

1. I have a views block displaying items
2. This block will be rendered in multiple areas on the site
3. The header text for the block must be customizable in each area it is rendered in on the site
4. For a clean UX, the header text must be entered when placing the block, ie in layout builder or on the block layout page (or anywhere else).

Solution:

<?php

declare(strict_types=1);

namespace Drupal\herons_base\Plugin\Block;

use Drupal\Core\Block\Attribute\Block;
use Drupal\Core\Block\BlockBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Creates a 
 */
#[Block(
  id: "abc_list_block",
  admin_label: new TranslatableMarkup("A listing of ABC block items"),
)]
class AbcBlocksListBlock extends BlockBase {

  /**
   * {@inheritdoc}
   */  
  public function defaultConfiguration() {
    return [
      'header_text' => [
        'value' => NULL,
        'format' => NULL,
      ],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {
    $header_text = this->configuration['header_text'];
    $form['header_text'] = [
      '#type' => 'text_format',
      '#title' => $this->t('Header Text'),
      '#default_value' => $header_text['value'],
      '#format' => $header_text['format'],
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {
    $this->configuration['hello_block_name'] = $form_state->getValue('header_text');
  }


  /**
   * {@inheritdoc}
   */
  public function build() {
    $header_text = this->configuration['header_text'];

    return [
      '#prefix' => '<div class="abc_list_wrapper">',
      '#suffix' => '</div>',
      'header' [
        '#prefix' => '<div class="header-text">',
        '#suffix' => '</div>',
        '#type' => 'processed_text',
        '#text' => $header_text['value'],
        '#format' => $header_text['format'],
      ],
      'view' => [
        '#type' => 'view',
        '#name' => 'abc_blocks',
        '#display_id' => 'listing_block',
      ],
    ];
  }

}

With this solution, the CKeditor enabled 'header text' field is made available on layout builder, and the block admin page, when placing a block, and renders the header when the block is rendered.

Thanks for sharing also @jaypan. It's in forum posts such as this, that images could be really useful, to demonstrate how the result looks like for the end user, in the GUI.

I am still hoping #2926532: Provide file upload for forums will happen.